In recent years, information terminal devices such as personal computers and servers and telecommunications devices such as internet routers and optical communication are required to process mass data at high speed and the speed and frequency of electric signals are increasingly becoming higher. Accordingly, laminates for printed wiring boards to be used for these devices are required to have a lower dielectric constant and a lower dielectric loss tangent, in particular to have a lower dielectric loss tangent, for the purpose of coping with the demand for high frequency.
For coping with these demands, conventionally, a cyanate ester resin (see, for example JP-A-2005-120173) and a polyphenylene ether resin (see, for example JP-A-2005-112981) are known as a resin for laminates for high frequency uses. As an epoxy resin to be used for high frequency uses, many reports say a biphenyl aralkyl type novolak epoxy resin is excellent in dielectric characteristics (see, for example, JP-A-10-237162, JP-A-2002-179761 and JP-A-2007-224162).
However, the above-mentioned biphenyl aralkyl novolak type epoxy resin has a problem in that a solution article thereof, which is obtained by dissolving the biphenyl aralkyl type novolak epoxy resin in an organic solvent, is poor in shelf life. As for the shelf life of a solution article of a resin composition, it is generally necessary that a solid content does not precipitate for at least three months when it is stored at 5° C. On the other hand, the solution product of the biphenyl aralkyl type novolak epoxy resin shows a precipitation of a solid content in a short period of time or about two weeks when stored at 5° C. Therefore, the stability of the quality of a prepreg or laminate which uses a varnish obtained by dissolving a resin composition containing the biphenyl aralkyl type novolak epoxy resin is a large problem.